Rethink and Design of Capacitor-Current-Feedback Active Damping for Grid-Following Inverters From a Passivity Enhancement Perspective

The effective region of capacitor-current-feedback active damping (CCF-AD) for suppressing the resonance of the LCL-filter for the grid-following inverter (GFLI) is commonly defined by the positive region of its equivalent resistor in parallel with the filter capacitor. This effective region is related to the delay of the digital control system. Therefore, previous research has focused on minimizing or compensating for the delay in the CCF-AD loop to extend its effective region. However, the effective region of CCF-AD does not serve as a sufficient stability condition for GFLI systems. Instead, the passivity of GFLI systems’ entire equivalent impedance can do it according to the frequency domain passivity theory. From the viewpoint of passivity stability, over-compensation of the delay may lead to deterioration rather than amelioration in the system’s stability. This article finds out that increasing or decreasing a small amount of delay for the positive or negative CCF-AD will sufficiently contribute to the overall passivity enhancement. Then, the new design guidelines are reformulated accordingly to enhance the overall passivity of GFLI systems. Finally, the theoretical expectations are verified by the experimental results.